1. Field of the Invention
The present invention relates to a method of molding an optical element such as an optical lens or a mirror, and an optical material for molding the optical element.
2. Related Background Art
Conventionally known as a technique for molding an optical element such as an optical lens or a mirror is press-molding. For example, as shown in FIG. 4, a preform A, which is an optical material, is disposed in a heated state at a molding position of a mold, and then an upper die B and a lower die C are moved so as to approach each other and carry out clamping, whereby an optical element is molded by the press-molding. When molding an optical element having a curved optically functional surface D by using the press-molding, the upper die B is brought into contact with the uppermost part E of the optically functional surface D, and then peripheries of the uppermost part E are brought into contact with and pressed against the upper die B, whereby the optical element is molded.
The molding method mentioned above, however, may be problematic in that molding cannot be carried out favorably when the optically functional surface of the optical element to be molded is an asymmetrical curved surface.
For example, as shown in FIG. 5, there is a case where the optically functional surface D is a curved surface which is asymmetrical about the center X of the optical element, and the uppermost part E of the optically functional surface D is not located at the center part F of the optically functional surface D. In this case, if the upper die B is brought into contact with the uppermost part E, and then peripheries of the uppermost part E are brought into contact with and pressed against the upper die B, the preform A will flow from the uppermost part E to its peripheries upon pressing (as indicated by arrows in FIG. 5).
In this case, while the form of optically functional surface is fully transferred to a region G between the uppermost part E and the end part closer thereto, it may not sufficiently be transferred to a region H on the opposite side between the uppermost part E and the end part farther therefrom, whereby air voids may occur in the region H.
For eliminating the problem mentioned above, it is an object of the present invention to provide an optical element molding method and an optical material for molding an optical element, which can favorably transfer an optically functional surface.
For achieving such an object, the present invention provides an optical element molding method comprising the step of pressing a heated optical material so as to mold an optical element having an asymmetrical optically functional surface; wherein a center part of a transfer surface of a molding die and a center part of the optical material are brought into contact with each other, and then a periphery of the center part of the optical material is brought into contact with the transfer surface so as to transfer a form of the transfer surface to the optical material.
Also, the present invention provides an optical material for molding an optical element, which is used for molding an optical element having an asymmetrical optically functional surface by pressing a heated optical material; wherein a tangential direction of a center part of a surface pressed against a transfer surface of a molding die is parallel to a tangential direction of a center part of the transfer surface.
In accordance with the present invention, when a molding die presses an optical material, the center part of the transfer surface of the molding die initially comes into contact with the center part of the optical material, and then the transfer surface gradually comes into contact with peripheries of the center part of the optical material, whereby the form of the transfer surface is transferred to the optical material. Therefore, the transfer surface of the molding die is favorably transferred to the pressing surface of the optical material without losing its balance, whereby air voids are prevented from occurring in the pressing surface of the optical material.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.